Pressure sensing guidewires

ABSTRACT

Medical devices and methods for making and using medical devices are disclosed. An example medical device may include a medical device for measuring blood pressure. The medical device may include an elongated shaft having a proximal region and a distal region. An optical fiber may extend along the proximal region. An optical pressure sensor may be coupled to the optical fiber. The optical pressure sensor may be disposed along the distal region. A centering member may be coupled to the optical fiber and positioned adjacent to the optical pressure sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S.Provisional Application Ser. No. 62/032,169, filed Aug. 1, 2014, theentirety of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure pertains to medical devices, and methods formanufacturing medical devices. More particularly, the present disclosurepertains to blood pressure sensing guidewires and methods for usingpressure sensing guidewires.

BACKGROUND

A wide variety of intracorporeal medical devices have been developed formedical use, for example, intravascular use. Some of these devicesinclude guidewires, catheters, and the like. These devices aremanufactured by any one of a variety of different manufacturing methodsand may be used according to any one of a variety of methods. Of theknown medical devices and methods, each has certain advantages anddisadvantages. There is an ongoing need to provide alternative medicaldevices as well as alternative methods for manufacturing and usingmedical devices.

BRIEF SUMMARY

This disclosure provides design, material, manufacturing method, and usealternatives for medical devices. An example medical device formeasuring blood pressure includes an elongated shaft having a proximalregion and a distal region. An optical fiber extends along the proximalregion. An optical pressure sensor is coupled to the optical fiber. Theoptical pressure sensor is disposed along the distal region. A centeringmember is coupled to the optical fiber and positioned adjacent to theoptical pressure sensor.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member may include a polymer.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member has a substantially circularcross-sectional shape.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member has a non-circular cross-sectional shape.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member includes a coil.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member is disposed at a proximal end of theoptical pressure sensor.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member is spaced from a proximal end of theoptical pressure sensor.

Alternatively or additionally to any of the examples above, in anotherexample, the shaft has a plurality of slots formed therein.

Alternatively or additionally to any of the examples above, in anotherexample, at least some of the slots are positioned adjacent to thecentering member.

Alternatively or additionally to any of the examples above, in anotherexample, the distal region has a distal inner diameter, wherein theproximal region has a proximal inner diameter, and wherein the distalinner diameter is greater than the proximal inner diameter.

Alternatively or additionally to any of the examples above, the distalregion of the shaft has a distal inner diameter, wherein the proximalregion of the shaft has a proximal inner diameter, and wherein thedistal inner diameter is larger than the proximal inner diameter.

Alternatively or additionally to any of the examples above, thecentering member is disposed within the shaft along the distal region.

Alternatively or additionally to any of the examples above, thecentering member is coupled to an outer surface of the optical fiber.

Alternatively or additionally to any of the examples above, thecentering member is coupled to an inner surface of the distal region ofthe shaft.

Alternatively or additionally to any of the examples above, the medicaldevice is a guidewire for measuring fractional flow reserve.

An example pressure sensing guidewire includes a tubular member having aproximal region and a distal region. The distal region has a distalinner diameter. The proximal region has a proximal inner diameter. Thedistal inner diameter is larger than the proximal inner diameter. Anoptical fiber extends within the tubular member along the proximalregion. An optical pressure sensor is coupled to the optical fiber. Theoptical pressure sensor is disposed within the tubular member along thedistal region. A centering member is disposed within the tubular memberalong the distal region. The centering member is coupled to an outersurface of the optical fiber. The centering member is coupled to aninner surface of the distal region of the tubular member.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member includes a coil.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member is disposed at a proximal end of theoptical pressure sensor.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member is spaced from a proximal end of theoptical pressure sensor.

Alternatively or additionally to any of the examples above, in anotherexample, the shaft has a plurality of slots formed therein and whereinat least some of the slots are positioned adjacent to the centeringmember.

An example medical device for measuring blood pressure includes anelongated shaft having a proximal region and a distal region. An opticalfiber extends along the proximal region. An optical pressure sensor iscoupled to the optical fiber. The optical pressure sensor is disposedalong the distal region. A centering member is coupled to the opticalfiber and positioned adjacent to the optical pressure sensor.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member includes a polymer.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member has a substantially circularcross-sectional shape.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member has a non-circular cross-sectional shape.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member includes a coil.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member is disposed at a proximal end of theoptical pressure sensor.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member is spaced from a proximal end of theoptical pressure sensor. Alternatively or additionally to any of theexamples above, in another example, the shaft has a plurality of slotsformed therein.

Alternatively or additionally to any of the examples above, in anotherexample, at least some of the slots are positioned adjacent to thecentering member.

Alternatively or additionally to any of the examples above, in anotherexample, the distal region has a distal inner diameter, wherein theproximal region has a proximal inner diameter, and wherein the distalinner diameter is greater than the proximal inner diameter.

An example pressure sensing guidewire includes a tubular member having aproximal region and a distal region. The distal region has a distalinner diameter. The proximal region has a proximal inner diameter. Thedistal inner diameter is larger than the proximal inner diameter. Anoptical fiber extends within the tubular member along the proximalregion. An optical pressure sensor is coupled to the optical fiber. Theoptical pressure sensor is disposed within the tubular member along thedistal region. A centering member is disposed within the tubular memberalong the distal region. The centering member is coupled to an outersurface of the optical fiber. The centering member is coupled to aninner surface of the distal region of the tubular member.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member includes a polymer.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member has a substantially circularcross-sectional shape.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member has a non-circular cross-sectional shape.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member includes a coil.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member is disposed at a proximal end of theoptical pressure sensor.

Alternatively or additionally to any of the examples above, in anotherexample, the centering member is spaced from a proximal end of theoptical pressure sensor.

Alternatively or additionally to any of the examples above, in anotherexample, the shaft has a plurality of slots formed therein.

Alternatively or additionally to any of the examples above, in anotherexample, at least some of the slots are positioned adjacent to thecentering member.

A pressure sensing guidewire for measuring fractional flow reserveincludes an elongate shaft having a proximal region and a distal region.The distal region has a distal inner diameter. The proximal region has aproximal inner diameter that is smaller than the distal inner diameter.The distal region has a plurality of slots formed therein. An opticalfiber extends within the shaft along the proximal region. An opticalpressure sensor is coupled to the optical fiber. The optical pressuresensor is disposed within the distal region of the shaft. A centeringmember is coupled to the optical fiber. The centering member is designedto reduce contact between an inner surface of the shaft and the opticalpressure sensor.

The above summary of some embodiments is not intended to describe eachdisclosed embodiment or every implementation of the present disclosure.The Figures, and Detailed Description, which follow, more particularlyexemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description in connection with the accompanyingdrawings, in which:

FIG. 1 is a partial cross-sectional side view of a portion of an examplemedical device;

FIG. 2 is a partial cross-sectional view of an example medical devicedisposed at a first position adjacent to an intravascular occlusion;

FIG. 3 is a partial cross-sectional view of an example medical devicedisposed at a second position adjacent to an intravascular occlusion;

FIG. 4 is a partial cross-sectional side view of a portion of an examplemedical device;

FIG. 5 is side view of a portion of an example medical device; and

FIG. 6 is side view of a portion of an example medical device.

While the disclosure is amenable to various modifications andalternative forms, specifics thereof have been shown by way of examplein the drawings and will be described in detail. It should beunderstood, however, that the intention is not to limit the invention tothe particular embodiments described. On the contrary, the intention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the disclosure.

DETAILED DESCRIPTION

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere inthis specification.

All numeric values are herein assumed to be modified by the term“about,” whether or not explicitly indicated. The term “about” generallyrefers to a range of numbers that one of skill in the art would considerequivalent to the recited value (i.e., having the same function orresult). In many instances, the terms “about” may include numbers thatare rounded to the nearest significant figure.

The recitation of numerical ranges by endpoints includes all numberswithin that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and5).

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. As used in this specification and theappended claims, the term “or” is generally employed in its senseincluding “and/or” unless the content clearly dictates otherwise.

It is noted that references in the specification to “an embodiment”,“some embodiments”, “other embodiments”, etc., indicate that theembodiment described may include one or more particular features,structures, and/or characteristics. However, such recitations do notnecessarily mean that all embodiments include the particular features,structures, and/or characteristics. Additionally, when particularfeatures, structures, and/or characteristics are described in connectionwith one embodiment, it should be understood that such features,structures, and/or characteristics may also be used connection withother embodiments whether or not explicitly described unless clearlystated to the contrary.

The following detailed description should be read with reference to thedrawings in which similar elements in different drawings are numberedthe same. The drawings, which are not necessarily to scale, depictillustrative embodiments and are not intended to limit the scope of theinvention.

During some medical interventions, it may be desirable to measure and/ormonitor the blood pressure within a blood vessel. For example, somemedical devices may include pressure sensors that allow a clinician tomonitor blood pressure. Such devices may be useful in determiningfractional flow reserve (FFR), which may be understood as the pressureafter a stenosis relative to the pressure before the stenosis (and/orthe aortic pressure).

FIG. 1 illustrates a portion of an example medical device 10. In thisexample, medical device 10 is a blood pressure sensing guidewire 10.However, this is not intended to be limiting as other medical devicesare contemplated including, for example, catheters, shafts, leads,wires, or the like. Guidewire 10 may include a tubular member or shaft12. Shaft 12 may include a proximal portion 14 and a distal portion 16.The materials for proximal portion 14 and distal portion 16 may vary andmay include those materials disclosed herein. For example, distalportion 16 may include a nickel-cobalt-chromium-molybdenum alloy (e.g.,MP35-N). Proximal portion 14 may include stainless steel. These are justexamples. Other materials may also be utilized.

In some embodiments, proximal portion 14 and distal portion 16 areformed from the same monolith of material. In other words, proximalportion 14 and distal portion 16 are portions of the same tube definingshaft 12. In other embodiments, proximal portion 14 and distal portion16 are separate tubular members that are joined together. For example, asection of the outer surface of portions 14/16 may be removed and asleeve 17 may be disposed over the removed sections to join portions14/16. Alternatively, sleeve 17 may be simply disposed over portions14/16. Other bonds may also be used including welds, thermal bonds,adhesive bonds, or the like. If utilized, sleeve 17 used to joinproximal portion 14 with distal portion 16 may include a material thatdesirably bonds with both proximal portion 14 and distal portion 16. Forexample, sleeve 17 may include a nickel-chromium-molybdenum alloy (e.g.,INCONEL).

A plurality of slots 18 may be formed in shaft 12. In at least someembodiments, slots 18 are formed in distal portion 16. In at least someembodiments, proximal portion 14 lacks slots 18. However, proximalportion 14 may include slots 18. Slots 18 may be desirable for a numberof reasons. For example, slots 18 may provide a desirable level offlexibility to shaft 12 (e.g., along distal portion 16) while alsoallowing suitable transmission of torque. Slots 18 may bearranged/distributed along distal portion 16 in a suitable mannerincluding any of those arrangements disclosed herein. For example, slots18 may be arranged as opposing pairs of slots 18 that are distributedalong the length of distal portion 16. In some embodiments, adjacentpairs of slots 18 may have a substantially constant spacing relative toone another. Alternatively, the spacing between adjacent pairs may vary.For example, more distal regions of distal portion 16 may have adecreased spacing (and/or increased slot density), which may provideincreased flexibility. In other embodiments, more distal regions ofdistal portion 16 may have an increased spacing (and/or decreased slotdensity). These are just examples. Other arrangements are contemplated.

A pressure sensor 20 may be disposed within shaft 12 (e.g., within alumen 22 of shaft 12). While pressure sensor 20 is shown schematicallyin FIG. 1, it can be appreciated that the structural form and/or type ofpressure sensor 20 may vary. For example, pressure sensor 20 may includea semiconductor (e.g., silicon wafer) pressure sensor, piezoelectricpressure sensor, a fiber optic or optical pressure sensor, a Fabry-Perottype pressure sensor, an ultrasound transducer and/or ultrasoundpressure sensor, a magnetic pressure sensor, a solid-state pressuresensor, or the like, or any other suitable pressure sensor.

As indicated above, pressure sensor 20 may include an optical pressuresensor. In at least some of these embodiments, an optical fiber or fiberoptic cable 24 (e.g., a multimode fiber optic) may be attached topressure sensor 20 and may extend proximally therefrom. An attachmentmember 26 may attach optical fiber 24 to shaft 12. Attachment member 26may be circumferentially disposed about and attached to optical fiber 24and may be secured to the inner surface of shaft 12 (e.g., distalportion 16). In at least some embodiments, attachment member 26 isproximally spaced from pressure sensor 20. Other arrangements arecontemplated.

In at least some embodiments, distal portion 16 may include a regionwith a thinned wall and/or an increased inner diameter that defines ahousing region 52. In general, housing region 52 is the region of distalportion 16 that ultimately “houses” the pressure sensor (e.g., pressuresensor 20). By virtue of having a portion of the inner wall of shaft 12being removed at housing region 52, additional space may be created orotherwise defined that can accommodate sensor 20.

In at least some embodiments, it may be desirable for pressure sensor 20to have reduced exposure along its side surfaces to fluid pressure(e.g., from the blood). Accordingly, it may be desirable to positionpressure sensor 20 along a landing region 50 defined along housingregion 52. Landing region 50 may be substantially free of slots 18 sothat the side surfaces of pressure sensor 20 have a reduced likelihoodof being deformed due to fluid pressures at these locations. Distal oflanding region 50, housing region 52 may include slots 18 that providefluid access to pressure sensor 20.

Moreover, one or more of slots 18 may define a fluid pathway that allowsblood (and/or a body fluid) to flow from a position along the exterioror outer surface of guidewire 10 (and/or shaft 12), through slots 18,and into the lumen 22 of shaft 12, where the blood can come into contactwith pressure sensor 20. Because of this, no additional sideopenings/holes (e.g., other than one or more slots 18, a single slot 18extending through the wall of shaft 12, and/or a dedicated pressure portor opening) may be necessary in shaft 12 for pressure measurement. Thismay also allow the length of distal portion 16 to be shorter thantypical sensor mounts or hypotubes that would need to have a lengthsufficient for a suitable opening/hole (e.g., a suitable “large”opening/hole) to be formed therein that provides fluid access to sensor20.

A tip member 30 may be coupled to distal portion 16. Tip member 30 mayinclude a shaping member 32 and a spring or coil member 34. A distal tip36 may be attached to shaping member 32 and/or spring 34. In at leastsome embodiments, distal tip 36 may take the form of a solder ball tip.Tip member 30 may be joined to distal portion 16 of shaft 12 with abonding member 46 such as a weld.

Shaft 12 may include a hydrophilic coating 19. In some embodiments,hydrophilic coating 19 may extend along substantially the full length ofshaft 12. In other embodiments, one or more discrete sections of shaft12 may include hydrophilic coating 19.

In use, a clinician may use guidewire 10 to measure and/or calculate FFR(e.g., the pressure after an intravascular occlusion relative to thepressure before the occlusion and/or the aortic pressure). Measuringand/or calculating FFR may include measuring the aortic pressure in apatient. This may include advancing guidewire 10 through a blood vesselor body lumen 54 to a position that is proximal or upstream of anocclusion 56 as shown in FIG. 2. For example, guidewire 10 may beadvanced through a guide catheter 58 to a position where at least aportion of sensor 20 is disposed distal of the distal end of guidecatheter 58 and measuring the pressure within body lumen 54. Thispressure may be characterized as an initial pressure. In someembodiments, the aortic pressure may also be measured by another device(e.g., a pressure sensing guidewire, catheter, or the like). The initialpressure may be equalized with the aortic pressure. For example, theinitial pressure measured by guidewire 10 may be set to be the same asthe measured aortic pressure. Guidewire 10 may be further advanced to aposition distal or downstream of occlusion 56 as shown in FIG. 3 and thepressure within body lumen 54 may be measured. This pressure may becharacterized as the downstream or distal pressure. The distal pressureand the aortic pressure may be used to calculate FFR.

It can be appreciated that an FFR system that utilizes an opticalpressure sensor in a pressure sensing guidewire may be navigated throughthe tortuous anatomy. This may include crossing relatively tight bendsin the vasculature. Because of this, and for other reasons, it may bedesirable of pressure sensing guidewire to be relatively flexible, forexample adjacent to the distal end. It can be appreciated that inrelatively flexible guidewires, bending the guidewire could result incontact between an inner surface of the guidewire and, for example, thepressure sensor. Such contact could lead to alterations and/ordeformations of the pressure sensor, potentially leading to pressurereading offsets. Disclosed herein are pressure-sensing guidewires withincreased flexibility. Furthermore, the guidewires disclosed herein mayalso include structural features that may help to reduce contact betweenthe pressure sensor and the inner surface of the guidewire and,therefore, help to reduce the possibility of pressure reading offsets.

FIG. 4 illustrates a portion of another example guidewire 110 that maybe similar in form and function to other guidewires disclosed herein.Guidewire 110 may include shaft 112 having proximal portion 114 anddistal portion 116. Distal portion 116 may have slots or slits 118formed therein. At least some of slits 118 may extend through only aportion of the wall of shaft 112. Pressure sensor 120 may be disposedwithin shaft 112. In at least some embodiments, pressure sensor 120 maybe an optical pressure sensor having optical fiber 124 coupled thereto.

A centering member 160 may be coupled to optical fiber 124. In general,centering member 160 may be disposed along distal portion 116 of shaft112 and may define a location where contact may occur with the innersurface of shaft 112. More particularly, when shaft 112 is bent,deflected, or otherwise deformed, the outer surface of centering member160 may come into contact with the inner surface of shaft 112. In doingso, centering member 160 may reduce the likelihood that inner surface ofshaft 112 may contact pressure sensor 120. Therefore, by includingcentering member 160, guidewire 110 may be less likely to have pressurereading offsets.

In at least some embodiments, centering member 160 may be positionedadjacent to pressure sensor 120. For example, centering member 160 maybe spaced a distance D from the proximal end of pressure sensor 120.Distance D may be on the order of about 1-20 mm, or about 1-10 mm, orabout 1-5 mm. These are just examples. Other distances are contemplated.In other embodiments, centering member 160 may be positioned adjacentthe distal end of pressure sensor 120.

The form of centering member 160 may vary. In some instances, centeringmember 160 may be a polymer member coupled to optical fiber 124. Thepolymer may include any of the polymers disclosed herein (e.g.,polyimide). The shape or form of centering member 160 may also vary. Forexample, centering member 160 may take the form of a cylindrical diskcoupled to optical fiber 124. However, a number of other shapes,lengths, and forms are contemplated. This may include centering members160 with a substantially circular cross-sectional shape, with anon-circular cross-sectional shape, or the like. The number of centeringmembers 160 may also vary. In some embodiments, only one centeringmember 160 may be utilized. In other embodiments, two, three, four,five, six, or more centering members 160 may be utilized. The centeringmember(s) 160 may be arranged in a variety of different locations(proximal, distal, immediately adjacent, etc.) relative to pressuresensor 120.

FIG. 5 illustrates another example centering member 260 taking the formof a coil. The form of the coil may also vary. For example, the coil mayhave an open pitch (e.g., with space between adjacent coil windings), aclosed pitch (e.g., where adjacent coil winding contact one another), orcombinations thereof. In some instances, more than one coiled centeringmember 260 may be utilized.

While FIGS. 4-5 illustrate centering member 160/260 as being spacedfrom, for example, a proximal end of pressure sensor 120, this is notintended to be limiting. For example, FIG. 6 illustrates another examplecentering member 360 that is positioned directly adjacent to pressuresensor 120. In this example, pressure sensor 120 is positioned againstpressure sensor 120.

The materials that can be used for the various components of guidewire10 (and/or other guidewires disclosed herein) and the various tubularmembers disclosed herein may include those commonly associated withmedical devices. For simplicity purposes, the following discussion makesreference to shaft 12 and other components of guidewire 10. However,this is not intended to limit the devices and methods described herein,as the discussion may be applied to other tubular members and/orcomponents of tubular members or devices disclosed herein.

Shaft 12 may be made from a metal, metal alloy, polymer (some examplesof which are disclosed below), a metal-polymer composite, ceramics,combinations thereof, and the like, or other suitable material. Someexamples of suitable metals and metal alloys include stainless steel,such as 304V, 304L, and 316LV stainless steel; mild steel;nickel-titanium alloy such as linear-elastic and/or super-elasticnitinol; other nickel alloys such as nickel-chromium-molybdenum alloys(e.g., UNS: N06625 such as INCONEL® 625, UNS: N06022 such as HASTELLOY®UNS: N10276 such as HASTELLOY® C276®, other HASTELLOY® alloys, and thelike), nickel-copper alloys (e.g., UNS: N04400 such as MONEL® 400,NICKELVAC® 400, NICORROS® 400, and the like),nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such asMP35-N® and the like), nickel-molybdenum alloys (e.g., UNS: N10665 suchas HASTELLOY® ALLOY B2®), other nickel-chromium alloys, othernickel-molybdenum alloys, other nickel-cobalt alloys, other nickel-ironalloys, other nickel-copper alloys, other nickel-tungsten or tungstenalloys, and the like; cobalt-chromium alloys; cobalt-chromium-molybdenumalloys (e.g., UNS: R30003 such as ELGILOY®, PHYNOX®, and the like);platinum enriched stainless steel; titanium; combinations thereof; andthe like; or any other suitable material.

As alluded to herein, within the family of commercially availablenickel-titanium or nitinol alloys, is a category designated “linearelastic” or “non-super-elastic” which, although may be similar inchemistry to conventional shape memory and super elastic varieties, mayexhibit distinct and useful mechanical properties. Linear elastic and/ornon-super-elastic nitinol may be distinguished from super elasticnitinol in that the linear elastic and/or non-super-elastic nitinol doesnot display a substantial “superelastic plateau” or “flag region” in itsstress/strain curve like super elastic nitinol does. Instead, in thelinear elastic and/or non-super-elastic nitinol, as recoverable strainincreases, the stress continues to increase in a substantially linear,or a somewhat, but not necessarily entirely linear relationship untilplastic deformation begins or at least in a relationship that is morelinear that the super elastic plateau and/or flag region that may beseen with super elastic nitinol. Thus, for the purposes of thisdisclosure linear elastic and/or non-super-elastic nitinol may also betermed “substantially” linear elastic and/or non-super-elastic nitinol.

In some cases, linear elastic and/or non-super-elastic nitinol may alsobe distinguishable from super elastic nitinol in that linear elasticand/or non-super-elastic nitinol may accept up to about 2-5% strainwhile remaining substantially elastic (e.g., before plasticallydeforming) whereas super elastic nitinol may accept up to about 8%strain before plastically deforming. Both of these materials can bedistinguished from other linear elastic materials such as stainlesssteel (that can also can be distinguished based on its composition),which may accept only about 0.2 to 0.44 percent strain beforeplastically deforming.

In some embodiments, the linear elastic and/or non-super-elasticnickel-titanium alloy is an alloy that does not show anymartensite/austenite phase changes that are detectable by differentialscanning calorimetry (DSC) and dynamic metal thermal analysis (DMTA)analysis over a large temperature range. For example, in someembodiments, there may be no martensite/austenite phase changesdetectable by DSC and DMTA analysis in the range of about −60 degreesCelsius (° C.) to about 120° C. in the linear elastic and/ornon-super-elastic nickel-titanium alloy. The mechanical bendingproperties of such material may therefore be generally inert to theeffect of temperature over this very broad range of temperature. In someembodiments, the mechanical bending properties of the linear elasticand/or non-super-elastic nickel-titanium alloy at ambient or roomtemperature are substantially the same as the mechanical properties atbody temperature, for example, in that they do not display asuper-elastic plateau and/or flag region. In other words, across a broadtemperature range, the linear elastic and/or non-super-elasticnickel-titanium alloy maintains its linear elastic and/ornon-super-elastic characteristics and/or properties.

In some embodiments, the linear elastic and/or non-super-elasticnickel-titanium alloy may be in the range of about 50 to about 60 weightpercent nickel, with the remainder being essentially titanium. In someembodiments, the composition is in the range of about 54 to about 57weight percent nickel. One example of a suitable nickel-titanium alloyis FHP-NT alloy commercially available from Furukawa Techno Material Co.of Kanagawa, Japan. Some examples of nickel titanium alloys aredisclosed in U.S. Pat. Nos. 5,238,004 and 6,508,803, which areincorporated herein by reference. Other suitable materials may includeULTANIUM™ (available from Neo-Metrics) and GUM METAL™ (available fromToyota). In some other embodiments, a superelastic alloy, for example asuperelastic nitinol can be used to achieve desired properties.

In at least some embodiments, portions or all of shaft 12 may also bedoped with, made of, or otherwise include a radiopaque material.Radiopaque materials are understood to be materials capable of producinga relatively bright image on a fluoroscopy screen or another imagingtechnique during a medical procedure. This relatively bright image aidsthe user of guidewire 10 in determining its location. Some examples ofradiopaque materials can include, but are not limited to, gold,platinum, palladium, tantalum, tungsten alloy, polymer material loadedwith a radiopaque filler, and the like. Additionally, other radiopaquemarker bands and/or coils may also be incorporated into the design ofguidewire 10 to achieve the same result.

In some embodiments, a degree of Magnetic Resonance Imaging (MRI)compatibility is imparted into guidewire 10. For example, shaft 12 orportions thereof may be made of a material that does not substantiallydistort the image and create substantial artifacts (i.e., gaps in theimage). Certain ferromagnetic materials, for example, may not besuitable because they may create artifacts in an MRI image. Shaft 12, orportions thereof, may also be made from a material that the MRI machinecan image. Some materials that exhibit these characteristics include,for example, tungsten, cobalt-chromium-molybdenum alloys (e.g., UNS:R30003 such as ELGILOY®, PHYNOX®, and the like),nickel-cobalt-chromium-molybdenum alloys (e.g., UNS: R30035 such asMP35-N® and the like), nitinol, and the like, and others.

A sheath or covering (not shown) may be disposed over portions or all ofshaft 12 that may define a generally smooth outer surface for guidewire10. In other embodiments, however, such a sheath or covering may beabsent from a portion of all of guidewire 10, such that shaft 12 mayform the outer surface. The sheath may be made from a polymer or othersuitable material. Some examples of suitable polymers may includepolytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE),fluorinated ethylene propylene (FEP), polyoxymethylene (POM, forexample, DELRIN® available from DuPont), polyether block ester,polyurethane (for example, Polyurethane 85A), polypropylene (PP),polyvinylchloride (PVC), polyether-ester (for example, ARNITEL®available from DSM Engineering Plastics), ether or ester basedcopolymers (for example, butylene/poly(alkylene ether) phthalate and/orother polyester elastomers such as HYTREL® available from DuPont),polyamide (for example, DURETHAN® available from Bayer or CRISTAMID®available from Elf Atochem), elastomeric polyamides, blockpolyamide/ethers, polyether block amide (PEBA, for example availableunder the trade name PEBAX®), ethylene vinyl acetate copolymers (EVA),silicones, polyethylene (PE), Marlex high-density polyethylene, Marlexlow-density polyethylene, linear low density polyethylene (for exampleREXELL®), polyester, polybutylene terephthalate (PBT), polyethyleneterephthalate (PET), polytrimethylene terephthalate, polyethylenenaphthalate (PEN), polyetheretherketone (PEEK), polyimide (PI),polyetherimide (PEI), polyphenylene sulfide (PPS), polyphenylene oxide(PPO), poly paraphenylene terephthalamide (for example, KEVLAR®),polysulfone, nylon, nylon-12 (such as GRILAMID® available from EMSAmerican Grilon), perfluoro(propyl vinyl ether) (PFA), ethylene vinylalcohol, polyolefin, polystyrene, epoxy, polyvinylidene chloride (PVdC),poly(styrene-b-isobutylene-b-styrene) (for example, SIBS and/or SIBS50A), polycarbonates, ionomers, biocompatible polymers, other suitablematerials, or mixtures, combinations, copolymers thereof, polymer/metalcomposites, and the like. In some embodiments the sheath can be blendedwith a liquid crystal polymer (LCP). For example, the mixture cancontain up to about 6 percent LCP.

In some embodiments, the exterior surface of the guidewire 10(including, for example, the exterior surface of shaft 12) may besandblasted, beadblasted, sodium bicarbonate-blasted, electropolished,etc. In these as well as in some other embodiments, a coating, forexample a lubricious, a hydrophilic, a protective, or other type ofcoating may be applied over portions or all of the sheath, or inembodiments without a sheath over portion of shaft 12, or other portionsof guidewire 10. Alternatively, the sheath may comprise a lubricious,hydrophilic, protective, or other type of coating. Hydrophobic coatingssuch as fluoropolymers provide a dry lubricity which improves guidewirehandling and device exchanges. Lubricious coatings improve steerabilityand improve lesion crossing capability. Suitable lubricious polymers arewell known in the art and may include silicone and the like, hydrophilicpolymers such as high-density polyethylene (HDPE),polytetrafluoroethylene (PTFE), polyarylene oxides,polyvinylpyrolidones, polyvinylalcohols, hydroxy alkyl cellulosics,algins, saccharides, caprolactones, and the like, and mixtures andcombinations thereof. Hydrophilic polymers may be blended amongthemselves or with formulated amounts of water insoluble compounds(including some polymers) to yield coatings with suitable lubricity,bonding, and solubility. Some other examples of such coatings andmaterials and methods used to create such coatings can be found in U.S.Pat. Nos. 6,139,510 and 5,772,609, which are incorporated herein byreference.

The coating and/or sheath may be formed, for example, by coating,extrusion, co-extrusion, interrupted layer co-extrusion (ILC), or fusingseveral segments end-to-end. The layer may have a uniform stiffness or agradual reduction in stiffness from the proximal end to the distal endthereof. The gradual reduction in stiffness may be continuous as by ILCor may be stepped as by fusing together separate extruded tubularsegments. The outer layer may be impregnated with a radiopaque fillermaterial to facilitate radiographic visualization. Those skilled in theart will recognize that these materials can vary widely withoutdeviating from the scope of the present invention.

Various embodiments of arrangements and configurations of slots are alsocontemplated that may be used in addition to what is described above ormay be used in alternate embodiments. For simplicity purposes, thefollowing disclosure makes reference to guidewire 10, slots 18, andshaft 12. However, it can be appreciated that these variations may alsobe utilized for other slots and/or tubular members. In some embodiments,at least some, if not all of slots 18 are disposed at the same or asimilar angle with respect to the longitudinal axis of shaft 12. Asshown, slots 18 can be disposed at an angle that is perpendicular, orsubstantially perpendicular, and/or can be characterized as beingdisposed in a plane that is normal to the longitudinal axis of shaft 12.However, in other embodiments, slots 18 can be disposed at an angle thatis not perpendicular, and/or can be characterized as being disposed in aplane that is not normal to the longitudinal axis of shaft 12.Additionally, a group of one or more slots 18 may be disposed atdifferent angles relative to another group of one or more slots 18. Thedistribution and/or configuration of slots 18 can also include, to theextent applicable, any of those disclosed in U.S. Pat. Publication No.US 2004/0181174, the entire disclosure of which is herein incorporatedby reference.

Slots 18 may be provided to enhance the flexibility of shaft 12 whilestill allowing for suitable torque transmission characteristics. Slots18 may be formed such that one or more rings and/or tube segmentsinterconnected by one or more segments and/or beams that are formed inshaft 12, and such tube segments and beams may include portions of shaft12 that remain after slots 18 are formed in the body of shaft 12. Suchan interconnected structure may act to maintain a relatively high degreeof torsional stiffness, while maintaining a desired level of lateralflexibility. In some embodiments, some adjacent slots 18 can be formedsuch that they include portions that overlap with each other about thecircumference of shaft 12. In other embodiments, some adjacent slots 18can be disposed such that they do not necessarily overlap with eachother, but are disposed in a pattern that provides the desired degree oflateral flexibility.

Additionally, slots 18 can be arranged along the length of, or about thecircumference of, shaft 12 to achieve desired properties. For example,adjacent slots 18, or groups of slots 18, can be arranged in asymmetrical pattern, such as being disposed essentially equally onopposite sides about the circumference of shaft 12, or can be rotated byan angle relative to each other about the axis of shaft 12.Additionally, adjacent slots 18, or groups of slots 18, may be equallyspaced along the length of shaft 12, or can be arranged in an increasingor decreasing density pattern, or can be arranged in a non-symmetric orirregular pattern. Other characteristics, such as slot size, slot shape,and/or slot angle with respect to the longitudinal axis of shaft 12, canalso be varied along the length of shaft 12 in order to vary theflexibility or other properties. In other embodiments, moreover, it iscontemplated that the portions of the tubular member, such as a proximalsection, or a distal section, or the entire shaft 12, may not includeany such slots 18.

As suggested herein, slots 18 may be formed in groups of two, three,four, five, or more slots 18, which may be located at substantially thesame location along the axis of shaft 12. Alternatively, a single slot18 may be disposed at some or all of these locations. Within the groupsof slots 18, there may be included slots 18 that are equal in size(i.e., span the same circumferential distance around shaft 12). In someof these as well as other embodiments, at least some slots 18 in a groupare unequal in size (i.e., span a different circumferential distancearound shaft 12). Longitudinally adjacent groups of slots 18 may havethe same or different configurations. For example, some embodiments ofshaft 12 include slots 18 that are equal in size in a first group andthen unequally sized in an adjacent group. It can be appreciated that ingroups that have two slots 18 that are equal in size and aresymmetrically disposed around the tube circumference, the centroid ofthe pair of beams (i.e., the portion of shaft 12 remaining after slots18 are formed therein) is coincident with the central axis of shaft 12.Conversely, in groups that have two slots 18 that are unequal in sizeand whose centroids are directly opposed on the tube circumference, thecentroid of the pair of beams can be offset from the central axis ofshaft 12. Some embodiments of shaft 12 include only slot groups withcentroids that are coincident with the central axis of the shaft 12,only slot groups with centroids that are offset from the central axis ofshaft 12, or slot groups with centroids that are coincident with thecentral axis of shaft 12 in a first group and offset from the centralaxis of shaft 12 in another group. The amount of offset may varydepending on the depth (or length) of slots 18 and can include othersuitable distances.

Slots 18 can be formed by methods such as micro-machining, saw-cutting(e.g., using a diamond grit embedded semiconductor dicing blade),electron discharge machining, grinding, milling, casting, molding,chemically etching or treating, or other known methods, and the like. Insome such embodiments, the structure of the shaft 12 is formed bycutting and/or removing portions of the tube to form slots 18. Someexample embodiments of appropriate micromachining methods and othercutting methods, and structures for tubular members including slots andmedical devices including tubular members are disclosed in U.S. Pat.Publication Nos. 2003/0069522 and 2004/0181174-A2; and U.S. Pat. Nos.6,766,720; and 6,579,246, the entire disclosures of which are hereinincorporated by reference. Some example embodiments of etching processesare described in U.S. Pat. No. 5,106,455, the entire disclosure of whichis herein incorporated by reference. It should be noted that the methodsfor manufacturing guidewire 110 may include forming slots 18 shaft 12using these or other manufacturing steps.

In at least some embodiments, slots 18 may be formed in tubular memberusing a laser cutting process. The laser cutting process may include asuitable laser and/or laser cutting apparatus. For example, the lasercutting process may utilize a fiber laser. Utilizing processes likelaser cutting may be desirable for a number of reasons. For example,laser cutting processes may allow shaft 12 to be cut into a number ofdifferent cutting patterns in a precisely controlled manner. This mayinclude variations in the slot width, ring width, beam height and/orwidth, etc. Furthermore, changes to the cutting pattern can be madewithout the need to replace the cutting instrument (e.g., blade). Thismay also allow smaller tubes (e.g., having a smaller outer diameter) tobe used to form shaft 12 without being limited by a minimum cuttingblade size. Consequently, shaft 12 may be fabricated for use inneurological devices or other devices where a relatively small size maybe desired.

It should be understood that this disclosure is, in many respects, onlyillustrative. Changes may be made in details, particularly in matters ofshape, size, and arrangement of steps without exceeding the scope of theinvention. This may include, to the extent that it is appropriate, theuse of any of the features of one example embodiment being used in otherembodiments. The invention's scope is, of course, defined in thelanguage in which the appended claims are expressed.

What is claimed is:
 1. A medical device for measuring blood pressure,comprising: an elongated shaft having a proximal region and a distalregion; wherein the proximal region has a first wall thickness; whereinthe distal region has a second wall thickness different from the firstwall thickness; an optical fiber extending along the proximal region; anoptical pressure sensor coupled to the optical fiber, the opticalpressure sensor being disposed along the distal region; and a centeringmember coupled to the optical fiber and positioned within the distalregion of the shaft at a position adjacent to the optical pressuresensor.
 2. The medical device of claim 1, wherein the centering memberincludes a polymer.
 3. The medical device of claim 1, wherein thecentering member has a substantially circular cross-sectional shape. 4.The medical device of claim 1, wherein the centering member has anon-circular cross-sectional shape.
 5. The medical device of claim 1,wherein the centering member includes a coil.
 6. The medical device ofclaim 1, wherein the centering member is disposed at a proximal end ofthe optical pressure sensor.
 7. The medical device of claim 1, whereinthe centering member is spaced from a proximal end of the opticalpressure sensor.
 8. The medical device of claim 1, wherein the shaft hasa plurality of slots formed therein.
 9. The medical device of claim 8,wherein at least some of the slots are positioned adjacent to thecentering member.
 10. The medical device of claim 1, wherein the distalregion has a distal inner diameter, wherein the proximal region has aproximal inner diameter, and wherein the distal inner diameter isgreater than the proximal inner diameter.
 11. A pressure sensingguidewire, comprising: a tubular member having a proximal region and adistal region; wherein the distal region has a distal inner diameter;wherein the proximal region has a proximal inner diameter; wherein thedistal inner diameter is larger than the proximal inner diameter; anoptical fiber extending within the tubular member along the proximalregion; an optical pressure sensor coupled to the optical fiber, theoptical pressure sensor being disposed within the tubular member alongthe distal region; a centering member disposed within the tubular memberalong the distal region; wherein the centering member is coupled to anouter surface of the optical fiber; and wherein the centering member iscoupled to an inner surface of the distal region of the tubular member.12. The guidewire of claim 11, wherein the centering member includes apolymer.
 13. The guidewire of claim 11, wherein the centering member hasa substantially circular cross-sectional shape.
 14. The guidewire ofclaim 11, wherein the centering member has a non-circularcross-sectional shape.
 15. The guidewire of claim 11, wherein thecentering member includes a coil.
 16. The guidewire of claim 11, whereinthe centering member is disposed at a proximal end of the opticalpressure sensor.
 17. The guidewire of claim 11, wherein the centeringmember is spaced from a proximal end of the optical pressure sensor. 18.The guidewire of claim 11, wherein the shaft has a plurality of slotsformed therein.
 19. The guidewire of claim 18, wherein at least some ofthe slots are positioned adjacent to the centering member.
 20. Apressure sensing guidewire for measuring fractional flow reserve, theguidewire comprising: an elongate shaft having a proximal region and adistal region; wherein the distal region has a distal inner diameter;wherein the proximal region has a proximal inner diameter that issmaller than the distal inner diameter; wherein the distal region has aplurality of slots formed therein; an optical fiber extending within theshaft along the proximal region; an optical pressure sensor coupled tothe optical fiber, the optical pressure sensor being disposed within thedistal region of the shaft; and a centering member coupled to theoptical fiber and disposed within the distal region of the shaft, thecentering member being designed to reduce contact between an innersurface of the shaft and the optical pressure sensor.